On Sun, Mar 18, 2018 at 9:18 AM, Nguyễn Thái Ngọc Duy [off-list ref] wrote:

+ifneq ($(or $(filter gcc6,$(COMPILER_FEATURES)),$(filter clang4,$(COMPILER_FEATURES))),)
+CFLAGS += -Wextra

Another thing we can add here is -Og instead of standard -O2 (or -O0
in my build), which is supported since gcc 4.8. clang seems to support
it too (mapped to -O1 at least for clang5) but I don't know what
version added that flag.
-- 
Duy